Ultrasonographic Prenatal Assessment of Position of Fetal Conus Medullaris

Abstract Background: With advancing technology in medical field, fetal images has become very convenient and cost-effective. Recent guidelines of fetal imaging has suggested to look for conus medullaris (CM) in the fetal antenatal scanning. This may help in early detection of neural tube defects (NTDs) which should be the purpose of antenatal scanning. A low-lying CM is defined as its position below L3 vertebra. This may suggest underlying congenital malformations. This study was done to locate fetal CM at various gestational ages (GAs) and to measure the CM to last sacral vertebral distance (CS distance) at various GA and to correlate with other GA ultrasonographic parameters such as biparietal diameter (BPD), head circumference (HC), abdominal circumference (AC), and femur length (FL). Methodology: Fetal antenatal scan images were utilized to locate the position of CM and to measure the distance between CM and last sacral vertebra (CS distance). The images were grouped as Group 1 (≤20 weeks of GA), Group 2 (21–30 weeks of GA), and Group 3 (31–40 weeks of GA). Results: A total of 110 fetal scan images were studied. In 77 images, CM location was found to be at L2. None of the images had a low-lying CM. There was a strong positive linear correlation between CS distance at all GAs with FL, BPD, HC, AC, and GA. Conclusions: CM position and CS distance are easily measurable in fetal antenatal scanning. It should be a routine to look for CM during antenatal scanning for early diagnosis of NTDs.